Recently, IEEE 802.11ac, which achieves a further increase in speed of the wireless LAN (local area network) standards IEEE 802.11, has been formulated by the IEEE (Institute of Electrical and Electronics Engineers Inc.). Currently, activities for the standardization of IEEE 802.11ax, which is a successor to IEEE 802.11ac, are being initiated. Along with the rapid spread of wireless LAN devices, studies regarding an increase in throughput per user in an environment where wireless LAN devices are densely arranged have also been. conducted in the standardization of IEEE 802.11ax.
A wireless LAN system is a system that determines, according to carrier sense (CS), whether a transmission is allowed or disallowed. If a reception interference level is lower than a threshold according to carrier sense, it is determined that a transmission is allowed, and if interference power that is higher than the threshold is received, a transmission is avoided.
In the standardization of IEEE 802.11ax, discussions have taken place over change or dynamic control of the carrier sense threshold value. In an environment where wireless LAN devices are densely arranged, increases in transmission opportunities for each device are expected to be brought about by raising the carrier sense threshold value. However, raising the carrier sense threshold value raises concern about an increase in interference level on the receiving side.
In NPL 1 interference control is exercised by dynamically changing a threshold value for carrier sense (carrier sense level, CCA level: clear channel assessment level). An example is a mechanism in which terminal apparatuses placed at a short distance from each other can have their transmission opportunities increased raising the CCA level. Raising the CCA level is assumed to cause an increase in the amount of interference that other terminal apparatuses suffer. However, the influence of interference can be reduced by the use of the beam forming of the transmitting terminal apparatus, MU-MIMO (multi-user multiple input multiple output, SDMA: spatial division multiple access), or a technology for interference suppression of the receiving terminal apparatus.
In the standardization of IEEE 802.11ax, discussions have taken place over a function of rendering the CCA level variable. For that reason, an IEEE 802.11ax-compliant terminal apparatus (ax terminal) is assumed to use a value that is different from the conventional CCA level.